1.The 2001 census in the United Kingdom
was carried out on 29 April 2001. Under Census and Devolution legislation there
were, in fact, three parallel censuses conducted in the United Kingdom: one in
England and Wales by the Office for National Statistics (ONS), one in Scotland
by the General Register Office for Scotland and one in Northern Ireland by the
Northern Ireland Statistics and Research Agency. The statements below are made
with respect to the census in England and Wales, but in many respects they
reflect the position in all three parts of the United Kingdom.

2.It is early to draw definitive
conclusions of how well the 2001 census went, but nevertheless some important
assessments can be made to help shape future censuses in the United Kingdom and
elsewhere. The census was conducted on time and early indications are that the
coverage (proportion of the population counted) should be at least as high as
in 1991 (98 per cent), if not better. This is despite carrying out the census
during the height of the foot-and-mouth disease outbreak and in the run-up to a
general election. The key measurement will be, however, how well the
differential undercount experienced in 1991 has been reduced.

3.Statements are provided with respect
to each of the issues on the agenda. Further details on the United Kingdom
censuses are available at www.statistics.gov.uk.

4.The census in England and Wales is
carried out under the 1920 Census Act and the 1991 Census Confidentiality Act.
These acts also apply to the census in Scotland. Similar legislation applies in
Northern Ireland. Separate primary legislation for each census was required for
censuses conducted in the United Kingdom before 1920.

5.The Census Acts permit the government
of the day to hold censuses at intervals of not less than five years. In
practice, full censuses have been held every 10 years since 1801 with the
exception of 1941.

6.For each census, two pieces of
secondary legislation are required to be passed by Parliament, a Census Order
and Census Regulations. This legislation sets out the questions to be asked,
who has to answer them and the arrangements for conducting the census. They
permit a temporary field force of enumerators and field managers to be
recruited. For the 2001 census, Census Order and Regulations were made and
approved during 2000.

7.The census is compulsory with the
exception of the question on religion.

8.The final approval of the census
therefore rests with Parliament. However, in leading up to this process, it was
important that all known stakeholders were consulted and their views taken into
account. This started in 1995, when a series of working groups was established
with key census users in central and local government and in the academic and
private sectors. Three working groups were established to consider content of
the census (questions to be asked), population definitions and output. The
first two were key to shaping the census proposals, upon which more formal
consultation was carried out with ONS’s established census advisory groups—one
for each census-user sector.

9.During 1997 and 1998 formal “business
cases” were sought from the key census users as to their needs in respect of
the questions to be asked in the census. Other potential census users were also
invited to make submissions. This was done so that the final proposals would be
based on sound needs—that is, the information was:

§Vital to the process of resource
allocation from central to local government;

§Key to the development of government
policy at a local as well as national level;

§Needed to help plan local services;
and

§Not available from any other source.

10.Parallel to this was a
question-testing programme whereby all new and substantially revised questions
were tested with the public. This enabled the most important stakeholders of
all to be involved: those who would complete the census questionnaires. Over 40
question tests were carried out in a variety of ways, from cognitive research
to a large-scale test of 100,000 households in 1997 and a census rehearsal of
150,000 households in 1999.

11.A key part of the question-testing
programme was to assess the burden placed on the public. Despite the fact that
the census is compulsory, the census offices need the cooperation of the
public. It was vital to this end that questions were seen as acceptable and
relevant and were framed in such a way that people were able to understand them
and complete them accurately. One of the key findings from this process was
that a question on income was not acceptable despite an overwhelming
requirement from census users for it to be asked. On the other hand, a question
on religion was seen as acceptable and a means of inclusivity.

12.A draft package emerged, which was
then put to ministers to make final proposals in the form of a White Paper to
Parliament in March 1999; it was subsequently approved by Parliament in 2000.

13.The process of consultation on the
whole worked very well, although at times it needed to be stressed that final
decisions did not rest with census users but with ministers and Parliament. The
final package of questions did all have demonstrated needs. The only question
with a strong need that was rejected was that on income, for the reasons stated
earlier.

14.Although the process did identify all
main census users, there were some complaints from other potential users and
pressure groups that they had not had the opportunity or did not know how to contribute
so that their voices could be heard in time. It is always difficult with an
exercise such as the census to keep up to date with change, as arrangements
need to be made well in advance.

15.A particular example of this was a
request very late in the day for a Welsh tick box to be included in the
question on ethnic group in Wales. This had not emerged at all during the
extensive consultation programme, but with devolution of some powers (but not
the census) to the Welsh Assembly, a single “British” category became less
acceptable. This proved quite difficult to handle in the months leading up to
the census—the census had, after all, already been approved by the Westminster
Parliament.

16.One possible approach is to produce a
set of initial proposals—a form of “Green Paper”—which would be formally
published by the government and upon which reactions and business cases would
be sought. It should be noted, however, that in the period between the
publication of the White Paper until well after parliamentary approval, there
was very little reaction to the government’s proposals. On the contrary, there
was support as demonstrated by the ease with which legislation was passed by
Parliament.

17.In 1992, the United Kingdom census
offices carried out a policy evaluation and reappraisal. This looked at the
needs for census-type information over the coming decades.It concluded that there was still a
requirement which would not be met by alternatives, and following a review of
the possible options for collecting the information, that a traditional census
was the best way to collect the information in 2001. A similar approach will be
necessary for the future, and currently work has just begun on whether there is
a need for a 2006 census.

18.Longer term, it is vital to assess the
needs for information of a type collected by a census at a local level on a
comparable basis across the country. This will then need to be looked at in
terms of how well these needs might be met. It is still doubtful in the United
Kingdom whether administrative records can yet be relied upon to provide the
basic numbers of where people are and how old they are, but a new division has
been established in ONS to undertake work to see how more use could be made of
administrative records. Considerable hurdles—moral, political and legal—will
need to be overcome in terms of data sharing, appropriate use of data and
ensuring that details are up to date. A further important consideration is that
the very groups of the population that the census has most difficulty in
counting are likely to be those for whom administrative data are of poor
quality or missing.

19.However, there is a growing need for
information at the neighbourhood (small-area) level in the United Kingdom to
support the government’s neighbourhood renewal policies. A neighbourhood
statistics service has been established to make statistics that are already
available more widely accessible and to explore new ways of meeting current and
future needs.

20.The strategic approach to census
taking in the United Kingdom has been to use the resources available in the
best possible way. The two main issues facing the United Kingdom in the
planning of the management of the census were the expected difficulty (and
which fully materialized) in recruiting field staff and the impact on the rest of
the statistical office of conducting such a huge operation—the extensive
build-up and run-down of staff employed on the census. This is particularly
true in the case of the census in the United Kingdom, which has traditionally
been held every 10 years.

21.Strategies, therefore, needed to be
adopted which minimized these operational risks while targeting our efforts at
our goals—to minimize the differential level of undercount in the census and to
produce consistent data of sufficient quality to meet needs. The adoption of a
postal response method, “one-number” census approach and using a
service-contract approach to processing and other census operations all
reflected these aims. Further details are given in other parts of this report.

22.The United Kingdom census offices
started planning for the next census in 1993.Quality was at the heart of this planning.An extensive research programme was set up to look at various
options within the scope of a traditional census: to issue and retrieve a form
from every household and person in the country on census night. There were a
significant number of drivers for change, including experience with the 1991
census, society, technology and customer needs and expectations.

23.Given the need to change following the
1991 census and developments since, the strategic approach to the census in the
United Kingdom was that we should adopt new technology where it was most
relevant to meeting needs. This applied particularly in map production,
processing and output. New methodologies were also necessary, and they are
described below and in the section on data evaluation.

24.In adopting new technology, it became
apparent during the testing phase that not all expertise lay within the census
offices. The strategy was to use the best available where possible. Processing
of the census was identified as a key area where new technology could help but
where expertise and flexible access to resources lay elsewhere, outside the
census offices.

25.An extensive open procurement exercise
was conducted, and Lockheed Martin was awarded the contract to carry out the
printing of census forms and the basic data capture and coding of data from the
completed forms. The procurement process was deliberately set up in such a way
that solutions to the basic job were sought—that is, a service, rather than the
supply of systems or software. This enabled the supplier to own the solution
and manage it appropriately. The printing of forms was part of the service to
enable Lockheed Martin to ensure that they were compatible with their own
image-recognition technology.

26.Other service contracts were let in
respect of the payroll for field staff, the public enquiry helpline, distribution
and collection of census forms and other material from field staff and printing
of other census material.

27.To assist in identifying households
and ensuring that enumerators find them all, good maps are essential.Two developments were made in the census in
England and Wales.Firstly, enumerator
maps were produced using new Geographic Information System (GIS) technology
based on Ordnance Survey's product Addresspoint™. This provided enumerators
with a customized map on a single sheet of paper, rather than several maps with
hand-drawn boundaries of varying scales, as in previous censuses.

28.Secondly, a list of addresses was
provided as a starting point for enumerators, but their instructions were still
to call at every address in their area to try and make contact to establish how
many households and people there were behind the front door. In areas of high
levels of multi-occupancy (that is, an address with more than one household),
enumerator workloads (that is, the number of addresses an enumerator was
expected to cover) were, on average, half the size of those in “easier” areas.

29.It was estimated that the 1991 census
counted some 98 per cent of the population. This included some 1.5 per cent of
people “imputed” in households known to exist but from which no census form was
received.While the overall level of
coverage was high in comparison to international standards, the level of
coverage varied considerably from area to area and from subgroup to
subgroup.This so-called differential
underenumeration led to a rethink about the entire approach to conducting the
census.

30.There had been significant societal
changes—that is, households and people were away from home more frequently, and
there had been a significant increase in the number of one-person households
and entry-phones into buildings. This made the enumerator’s task of collecting
forms that much more difficult.

31.Since 1991, the research programme on
data collection focused on the issue of maximizing coverage and particularly on
reducing the bias in the resulting count.This meant that our efforts and resources had to be targeted at those
households and people with the greatest propensity to not comply with the
census—single-person person households, households in multi-occupancy, young
men, students, the elderly and ethnic minorities.

32.A number of initiatives were made.
Firstly, the 2001 census was conducted on an entirely resident basis.In previous censuses, people were counted
where they were on census night and
where they were resident if different.People away from home on census night—some 1.5 million in 1991—were
required to have information about them supplied twice. However, there was some
evidence that people away on census night understandably felt they had already
complied with the census and their details were not recorded at their home
address. Further, the information on the number of “visitors” (that is,
non-residents) to an area was not extensively used.So the first step was to reduce this burden on the public.In 2001, people were asked to supply
information only at their home (resident) address.

33.Secondly, the public was asked to post
their census forms back. Prepaid return envelopes were provided.Tests had shown that we might expect some 60
per cent to 70 per cent of households to respond by post. In reality, some 88
per cent in 2001 posted their form back, a very pleasing result.

34.It should be emphasized that
enumerators still delivered the census forms and “followed up” those households
who had not returned a form. This “follow-up” procedure was due to start some
four to five days after census day, but in practice it had to be delayed by
about a week because of the considerably higher than expected postal response.
Tests had shown this to be the best strategic approach, allowing enumerator
resources at “follow-up” to be targeted at those areas which were likely to
have a lower postback response—inner cities, areas of high elderly population,
areas of high ethnic minority population, areas with high levels of
multi-occupied buildings and so forth.

35.A community liaison programme was
established. This was more than part of the publicity strategy for the 2001
census. The objective was to establish links at national and, more
particularly, local levels to “sell” the benefits of the census to different
communities and give assistance where needed.This programme was cascaded via the census area managers, the top level
of the census field force.

36.Students are another particularly
difficult group to enumerate in a census. There were distinct advantages, from
a user perspective, in counting students at their term-time (as opposed to
vacation) address.It is the term-time
population of an area that is used in allocating resources from central to
local government.To help achieve an
accurate term-time count, the 2001 census was carried out at a time outside
vacation periods for the majority of universities and colleges. Students still
needed some encouragement, however, and this is where publicity played a role.

37.The publicity strategy for the census
was, of course, vital.This raised
awareness of the public to the purpose of the census and reminded them to
return their form.While the main
messages were just this, more specific targeting towards difficult-to-enumerate
groups was needed in the form of posters and information leaflets directed
towards students, the ethnic minority population (including translations into
24 different languages) and other difficult-to-enumerate groups.

38.The level of contract management was
considerably increased from previous censuses. While the need to recruit
significant numbers of temporary staff to conduct and process the census has
been considerably reduced, new skills were required to manage the different
levels of contracts and the interfaces between them. This has been demanding,
particularly for some contracts. Consultant advisors have been employed to help
this process, but one of the key lessons has been the difficulty of managing
the interfaces between the different suppliers. Ensuring that census forms were
printed to the right timescales so they could be distributed to field staff is
one such example.

39.Recruitment of field staff proved a
much harder job than previously despite the fact that the numbers required (some
75,000 in total in England and Wales) were reduced by one third from those
employed in 1991. Today’s society means that people have less spare time and
perhaps less of a community spirit to do the job. In the end, sufficient
numbers were recruited, but it was a considerable challenge in London in
particular. The number of applicants to posts in some areas was as low as one
to one. For future censuses, we will undoubtedly need to look to alternative
ways to reduce the need for so many field staff.

40.The new-style maps were well received
and enabled enumerators to identify their areas much more easily than hitherto.
There was an overwhelming postal response to the census, and it was clear that
the right approach had been taken in the method of response for the majority of
the public in today’s busy lifestyles.

41.The high level of postal response did,
however, cause problems at the local level for field staff in being able to
identify those households who had not posted their forms so they could be
“followed up”. Problems were encountered in managing this in real time. The
management information systems used by census field staff were inadequate in
providing information on how the process was going, thus hampering the ability
of managers at the centre and regionally to reallocate resources where they
were needed. In hindsight, a longer period before follow-up should have been
allowed, coupled with the deployment of personal computers to all field
managers, rather than relying on a one-way information system using touch-tone
technology.

42.The pitfalls of changing methodology
were also illustrated, particularly when many of the field staff employed had
worked on previous censuses when all forms were collected by hand. Training of
field staff was extensive and on the whole well received, but perhaps a more
strategic and less procedural approach was needed to make the field staff feel
more involved and aware of the need for methodological change.

43.The census was conducted during a
major outbreak of foot-and-mouth disease. This necessitated an urgent
assessment of whether the census should continue. Plans were well advanced and
it was concluded that with the adoption of special measures it was preferable
to continue. Special procedures and publicity were organized and distributed,
which worked well. There were inevitably scare story reports of enumerators’
transmitting the disease, but these proved unfounded and were dealt with
efficiently and sympathetically.

44.Crisis management of this and other
issues that arise during the conduct of the census are a key element of
managing the census. We developed lines to take on a number of issues that we
thought might happen from past experience, such as lost forms. These proved
useful in providing an overall line to take, but, as ever, each case is unique
and needs an individual response, be it to an individual or the media. This is
what happened.

45.Media response to the census was
mixed. Tabloid newspapers were, following efforts by the publicity team,
supportive, but broadsheet and mainstream newspapers were considerably less so
and at times were overly and unfairly critical. This was not helped because of
the lead-up to the general election. The strategy taken was to respond to
issues that were clearly incorrect. Media management was a short-term and
demanding aspect of the census.

46.In an exercise as large and complex as
the census, it is inevitable that errors will occur.These are caused mainly at the form-completion stage, through
answers’ being missed or inconsistent answers given (such as someone who
describes himself as married but is only 10 years old).It is simply not practical, at least in the
United Kingdom, to check every form with every household, so it has been
traditional for editing routines to be used in processing.Editing and imputation techniques, similar
to those used in previous censuses, will be used to “rectify” and estimate such
data.The approach to be taken in 2001
builds on the original Fellegi and Holt principles (Fellegi and Holt, 1976).

47.In summary, answers to questions that
are considered to be inconsistent with one another are assessed in a series of
logical rules.An automatic
decision-making process using other information on the form decides which
answer is most likely to be incorrect based on the principle of making least
change to the data.The answer to the
question is then either set to missing or, where there is only one appropriate
answer, that answer is substituted.

48.Imputation of missing answers follows
by a route whereby the answer to the question is copied from a similar person
or household (called the “donor” person or household) in the same or nearby
geographical area.Unlike in 1991, it
is intended that when a census form contains several missing answers, one
“donor” person or household be used.This has been demonstrated to maintain the statistical integrity of the
marginal and joint distributions better than using several “donors” to supply
several missing answers for one person or household record.

49.Following the editing and imputation
of returned forms comes the estimation of numbers and characteristics of
households and people missed entirely by the census. Despite the initiatives at
the data-collection stage, it is inevitable that some people and households
will not be counted, and some subgroups of the population have a greater
propensity to be missed than others.Before I describe the substantial innovations for 2001 in this respect,
I will return to the experiences in 1991.

50.It is traditional in many
census-taking countries for the census to be “followed up” by a
post-enumeration survey(PES) to
estimate the number of people missed by the census. This was the approach taken
in 1991 in Britain with the Census Validation Survey (as the PES was then
known).This survey had a dual purpose:
to measure both coverage (the number of people counted) and the quality of
answers to census questions.Some
20,000 addresses were sampled.

51.Unfortunately, the Census Validation
Survey (CVS) failed to find many of the people missed by the census. When the
CVS estimates of the census undercount and the census counts themselves were
analysed (particularly by looking at the proportions of males to females), it
was evident that a more reliable indicator of the national figure would be
provided by the existing series of population estimates based on the 1981
census.Further, the CVS (mainly
because of its size) was unable to provide much breakdown of the undercount
across the country, although some information was used to “re-base” the local
population estimates on the 1991 census, constrained to the national estimate.
This was unsatisfactory all round, as insufficient information was available to
guide census users on the level and nature of the undercount, particularly at
the local level.Only broad guidance
could be provided.Further, several
figures on the total population of the country were actually produced, thus
adding to the confusion.

52.The United Kingdom census offices, in
response to the problems in 1991, have tackled this in earnest. A separate
research programme was set up in 1996 to evaluate different methodologies and
to plan the approach well in advance. The objective of the “One-Number Census”
(ONC) programme (as it is known) is to estimate the level of underenumeration
and to integrate this with the census counts so that all census outputs sum to
one number—the national estimate of the population on census day.The methodological research has included
looking at administrative records and whether they could be used to aid the
estimation of the census undercount.It
was clear, however, that no such records were available of the required
quality, supporting the conclusions arrived at in the early 1990s.The approach has been therefore to use a
post-enumeration survey but one which concentrates exclusively on coverage and
which was much bigger to give the statistical resilience that was not there in
the 1991 census.

53.A Census Coverage Survey (CCS) of some
300,000 households was carried out some three to four weeks after the census.
It encompassed an intensive re-enumeration of some 20,000 postcode units
(average size of 15 households) across the country.The sample was designed to produce direct estimates for some 100
“design groups” (average population size of 500,000 people). The sample was
stratified by a “hard-to-count” index so that estimates can be made separately
according to the likely level of underenumeration. The survey comprised short
doorstep interviews of around 10-15 minutes each.

54.The information from the survey will
be combined with that from the census and estimates of underenumeration made at
the design-group level using a combination of dual-system and regression-based
estimators.These will then be cascaded
using synthetic estimation techniques to the local/unitary authority level
(average population size of 120,000) to provide the new base of local
population estimates by age and sex.

55.The final step of the ONC process is
to estimate the probabilities of households and people being missed at the
local level by type of household and person.Imputation of households and people according to these probabilities
will follow to produce a fully adjusted census database.This final process will be constrained to
the estimates produced at the local/unitary authority level. Further
information on the methodology for the ONC is available at http://www.ons.gov.uk)

56.The end result of this innovative
census-processing stage will be a database comprising both individuals and
households counted by the census and synthetic households and people
representing those estimated to have been missed.It forms the database to be used to produce the output.

57.Demographic analysis will be used in
the United Kingdom to help assure the quality of estimates produced by the
Census/CCS dual-system approach. The Census/CCS estimates will not be
constrained to the demographic estimates; the latter will purely be used to
highlight potential problems with the Census/CCS estimates. For example,
sex-ratio analysis based on estimates of the population from the previous
census and age distributions will help to identify whether particular sex/age
groups have been under- or overestimated.

58.As much as possible will be done at a
regional and local level, but more reliable checks can really be carried out
only at the national level because of the hitherto unreliability of comparable
data at subnational levels. For example, information at a national level from
administrative records for pensioners and children will provide further
diagnostic checks, but because they are based on benefit and pension records
and because payments of child benefit and pensions are made in many cases directly
into bank accounts, the address of the recipient is often not strictly
necessary.